With shock absorbers employed in vehicles such as automobiles and motor cycles, it is desirable to variably control damping force freely according to the driving conditions and the like.
Conventionally, therefore, a damping force variable hydraulic shock absorber 60 as shown, for example, in FIG. 10 has been employed. The shock absorber 60 is of the following construction. That is, it includes upper and lower oil chambers 63, 64 defined by a piston 62 within a cylinder 61, an auxiliary oil chamber 62b formed within the piston 62, and a main valve 65 disposed within the auxiliary oil chamber for opening and closing a main passageway 62a which communicates with the two oil chambers 63, 64. The auxiliary oil chamber 62b is adapted to communicate with the upper and lower oil chambers 63, 64 through a check valve 62c. A pilot passage 62d for allowing the pressure within the auxiliary oil chamber 62b to escape is provided which can be opened and closed by a pilot valve 66, the biasing force of the pilot valve 66 in the direction of closing movement being adjustable by means of an electromagnetic coil 67.
With this prior art shock absorber 60, by controlling power supply to the electromagnetic coil 67 according to the driving conditions and the like, it is possible to control the closing force of the pilot valve 66 with respect to the pilot passage 62d and, in turn, the opening and closing of the main valve 65. Thus, the damping force of the working fluid, as it is generated when the fluid flows through an open clearance between the main valve 65 and the valve seat for the main passageway 62a, is variably controlled.
However, such prior art shock absorber 60 involves problems. One problem is low response, and another is that the pilot valve 66 is liable to axial vibration. Such problems are believed to be due to the following fact. That is, in the prior art shock absorber 60, the abutment surface (sealing surface) of the pilot valve 66 for contact with the valve seat 62e is of conical shape so that the area of opening defined by the pilot valve 66 and valve seat 62e is small relative to same strokes of the pilot valve 66.
The present invention has been developed in view of these problems with the prior art and, therefore, it is an object of the invention to provide a damping force variable hydraulic shock absorber which can exhibit improved response and inhibit pilot valve vibrations.